1. Field of the Invention
The present invention relates to a semiconductor device configured to control a static actuator utilizing MEMS (Micro Electro Mechanical Systems).
2. Description of the Related Art
In recent years, MEMS is receiving attention as one of technologies for achieving a miniaturization, a weight reduction, a lowering of power consumption, and an increased functionality in electronic equipment. This MEMS is a system that uses a silicon process technology to integrate minute mechanical elements and electronic circuit elements.
A structure of a static actuator utilizing this kind of MEMS technology is disclosed in U.S. Pat. No. 5,578,976. To set the static actuator to a closed state (a state in which an upper electrode and a lower electrode are in contact with an insulating film interposed therebetween), a potential difference is applied between the upper electrode and the lower electrode so that an electrostatic attractive force between these electrodes exceeds an elastic force of a movable portion to which the upper electrode is fixed.
In such a closed state of the static actuator, a state is reached where the upper electrode and the lower electrode are in contact with the insulating film interposed therebetween, thereby an electrostatic capacitance between the upper electrode and the lower electrode being greater than when in an open state. At this time, a charge may be injected into and trapped in the insulating film through FN (Fowler-Nordheim) tunneling or the Poole-Frenkel mechanism. This phenomenon is called dielectric-charging of the static actuator.
Further, when an amount of charge trapped in the insulating film due to dielectric-charging becomes greater than or equal to a certain value, the upper electrode is attracted by the charge in the insulating film and it becomes impossible to change the static actuator from the closed state to the open state, even if the potential difference between the upper electrode and the lower electrode is set to 0V. This phenomenon is called stiction due to dielectric charging.
To avoid such stiction, there is, for example, a method of inverting a polarity of potential between the upper electrode and the lower electrode (refer to G. M. Rebeiz: “RF MEMS Theory, Design, and Technology”, Wiley-Interscience, 2003, pp. 190-191).
When the above-described method is used, there is a problem that a cycle for inverting the polarity is faster than necessary, leading to an increase in power consumption.
Additionally in the case of using the above-described method, if electrodes of a plurality of actuators, capacitors, and the like, are disposed adjacently, noise accompanying the above-described polarity inversion is generated along with a signal applied to those electrodes.